CMP is one place to buy ammo, however there a hoops you have go through. The American Eagle is good. Also stay within 147 to 168 grains on bullet weight and 2700 PFS max to prevent oprod excessive wear or damage.
If you reload, use the Hornady 8th or so edition reloading manual, there is section there specific for service rifles, M1's and M14/M1A's
You can browse CMP Forum
http://forums.thecmp.org/If your interested in replacing the barrel, I have newer (CBI) Criterion Barrel Inc with only 64 rounds through it. I bought it new from CMP ; after the 64 rounds I decided to replace it with a .308win barrel.